﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Text;

namespace iTelluro.Explorer.Domain.Seedwork.Specification
{
    public static class ExpressionBuilder
    {
        public static Expression<T> Compose<T>(this Expression<T> first, Expression<T> second, Func<Expression, Expression, Expression> merge)
        {
            //build parameter map(from parameters of second to parameters of first
            var map = first.Parameters.Select((f, i) => new { f, s = second.Parameters[i] }).ToDictionary(p => p.s, p => p.f);

            //replace parameters in second lambda expression with parameters from the first
            var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);
            //apply composition of lambda expression bodies to parameters from the  first expression
            return Expression.Lambda<T>(merge(first.Body,secondBody),first.Parameters);
        }

        /// <summary>
        /// And operator
        /// </summary>
        /// <typeparam name="T">Type of params in expression</typeparam>
        /// <param name="first">Right Expression in AND operation</param>
        /// <param name="second">Left Expression in And operation</param>
        /// <returns>New AND expression</returns>
        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
        {
            return first.Compose(second, Expression.And);
        }
        /// <summary>
        /// Or operator
        /// </summary>
        /// <typeparam name="T">Type of param in expression</typeparam>
        /// <param name="first">Right expression in OR operation</param>
        /// <param name="second">Left expression in OR operation</param>
        /// <returns>New Or expressions</returns>
        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
        {
            return first.Compose(second, Expression.Or);
        }
    }
}
